Systems and methods for synthesis of nitric oxide

ABSTRACT

Systems and methods for producing nitric oxide (NO) to be used in medical applications are provided. In some embodiments, systems and methods are provided for a NO generator that is capable of generating a desired concentration of NO to be provided to a respiratory system for inhalation by a patient.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is based on, claims priority to, andincorporates herein by reference in their entirety, U.S. ProvisionalPatent Application No. 62/065,825, filed Oct. 20, 2014, and entitled“Producing Nitric Oxide for Inhalation by Electric Discharge in Air,”and U.S. Provisional Patent Application No. 62/077,806, filed Nov. 10,2014, and entitled “Synthesis of Nitric Oxide.”

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND

The disclosure relates generally to the electrical plasma synthesis ofnitric oxide (NO) from gases and, more specifically, to systems andmethods for producing safe NO to be used in medical applications.

NO is a crucial mediator of many biological systems, and is known tocontrol the level of systemic and pulmonary artery blood pressure, helpthe immune system kill invading parasites that enter cells, inhibit thedivision of cancer calls, transmit signals between brain cells, andcontribute to the death of brain cells that debilitates people withstrokes or heart attacks, among other things. NO mediates the relaxationof smooth muscle present, for example, in the walls of blood vessels,bronchi, the gastrointestinal tract, and urogential tract.Administration of NO gas to the lung by inhalation has been shown toproduce localized smooth muscle relaxation within the lung's bloodvessels and is widely used to treat pulmonary hypertension, pneumonia,hypoxemic respiratory failure of a newborn, etc. without producingsystemic side effects.

Inhaling NO can immediately produce potent and selective pulmonaryvasodilation that improves the matching of ventilation with perfusion,thereby increasing an injured lung's oxygen transport efficiency, andbreathing NO can raise the arterial oxygen tension. Breathing NOproduces the rapid onset of pulmonary vasodilator action occurringwithin seconds of commencing breathing with the absence of systemicvasodilatation. Once inhaled, NO diffuses through the pulmonaryvasculature into the bloodstream, where it is rapidly inactivated bycombination with hemoglobin (the NO dioxygenation reaction). Therefore,the vasodilatory effects of inhaled NO are limited to these pulmonarytherapeutic advantages in the treatment of acute and chronic pulmonaryhypertension. Inhaled NO can also be used to prevent ischemiareperfusion injury after percutaneous coronary intervention in adultswith heart attacks. Furthermore, inhaled NO can produce systemicanti-inflammatory and anti-platelet effects by increasing the levels ofcirculating NO biometabolites and by other mechanisms, such as theoxidation of circulating ferrous hemoglobin in the plasma. Finally, NOhas known anti-microbial activity.

BRIEF SUMMARY

The present disclosure provides systems and methods for producing nitricoxide (NO) to be used in medical applications. Specifically, systems andmethods are provided for a NO generator that is capable of generating adesired concentration of pure and safe NO to be provided to arespiratory system for inhalation by a patient.

In one aspect, the present disclosure provides an apparatus forgenerating nitric oxide including one or more pairs of electrodes, afilter arranged downstream of the electrodes, and a scavenger arrangeddownstream of the electrodes. The apparatus further includes one or moresensors configured to measure at least one of a flowrate of gas, anoxygen concentration upstream of the electrodes, a nitric oxideconcentration downstream of the scavenger, and a nitrogen dioxideconcentration downstream of the scavenger, and a controller incommunication with the electrodes and the one or more sensors andconfigured to supply an electrical signal to the electrodes thatcontrols timing and sparking characteristics of the electrodes. Thesparking characteristics of the electrodes determine a concentration ofnitric oxide generated by the electrodes.

In some embodiments, the electrodes comprise at least one of tungstencarbide, carbon, nickel, iridium, titanium, rhenium, and platinum

In some embodiments, the electrodes comprise iridium.

In some embodiments, the scavenger is fabriced from calcium hydroxide.

In some embodiments, the one or more sensors include an airway flowmeterarranged downstream of the electrodes, an oxygen sensor arrangedupstream of the electrodes, a nitric oxide sensor arranged downstream ofthe scavenger, and a nitrogen dioxide sensor arranged downstream of thescavenger.

In some embodiments, an ignition coil is in communication with thecontroller and the electrodes.

In some embodiments, the controller is further configured to instructthe ignition coil to supply stored electrical energy to the electrodes.

In some embodiments, the electrical signal supplied to the electrodescontrols at least one of a number of electrode spark groups per second,a number of individual electrode sparks per spark group, a time betweenindividual electrode sparks, and a pulse duration.

In some embodiments, the controller is further configured to vary atleast one of the number of electrode spark groups per second, the numberof individual electrode sparks per spark group, the time betweenindividual electrode sparks, and the pulse duration in response tofeedback from the one or more sensors.

In some embodiments, the apparatus further comprises a gas pump arrangedupstream of the electrodes.

In some embodiments, the one or more sensors provide an indication ofinspiration.

In some embodiments, the controller is further configured to supply theelectrical signal to the electrodes in response to detectinginspiration.

In some embodiments, the filter is configured to filter particlesflowing downstream of the electrodes with a diameter greater thanapproximately 0.22 micrometers.

In another aspect, present disclosure provides an apparatus forgenerating nitric oxide to be integrated into a respiratory systemhaving a breathing apparatus, an inspiratory line, and an airwayflowmeter arranged on the inspiratory line. The apparatus includes oneor more pairs of electrodes in gaseous communication with theinspiratory line, a filter arranged downstream of the electrodes, and ascavenger arranged downstream of the electrodes. The apparatus furtherincludes one or more sensors configured to measure at least one of anoxygen concentration upstream of the electrodes, a barometric pressure,a nitric oxide concentration downstream of the scavenger, and a nitrogendioxide concentration downstream of the scavenger, and a controller incommunication with the electrodes, the one or more sensors, and theairway flowmeter, and configured to supply an electrical signal to theelectrodes that controls timing and sparking characteristics of theelectrodes. The sparking characteristics of the electrodes determine aconcentration of nitric oxide generated by the electrodes.

In some embodiments, the electrodes are arranged between an inlet and anoutlet, the outlet is coupled to the inspiratory line.

In some embodiments, the electrodes are at least partially integratedinto the inspiratory line.

In some embodiments, the filter is arranged on the inspiratory line.

In some embodiments, the scavenger is arranged on the inspiratory line.

In some embodiments, the electrodes comprise at least one of tungstencarbide, carbon, nickel, iridium, titanium, rhenium, and platinum.

In some embodiments, the electrodes comprise iridium.

In some embodiments, the scavenger is fabricated from calcium hydroxide.

In some embodiments, the one or more sensors include an oxygen sensorarranged upstream of the electrodes, a nitric oxide sensor arrangeddownstream of the scavenger, and a nitrogen dioxide sensor arrangeddownstream of the scavenger.

In some embodiments, an ignition coil is in communication with thecontroller and the electrodes.

In some embodiments, the controller is further configured to instructthe ignition coil to supply stored electrical energy to the electrodes.

In some embodiments, the electrical signal supplied to the electrodescontrols at least one of a number of electrode spark groups per second,a number of individual electrode sparks per spark group, a time betweenindividual electrode sparks, and a pulse duration.

In some embodiments, the controller is further configured to vary atleast one of the number of electrode spark groups per second, the numberof individual electrode sparks per spark group, the time betweenindividual electrode sparks, and the pulse duration in response tofeedback from the one or more sensors.

In some embodiments, the apparatus further comprises a gas pump arrangedupstream of the electrodes.

In some embodiments, the airway flowmeter provides an indication ofinspiration.

In some embodiments, the controller is further configured to supply theelectrical signal to the electrodes in response to detectinginspiration.

In some embodiments, the filter is configured to filter particlesflowing downstream of the electrodes with a diameter greater thanapproximately 0.22 micrometers.

In some embodiments, the breathing apparatus comprises one of aventilator system, a continuous positive airway pressure (CPAP) system,a high frequency oscillatory ventilator (HFOV), a face mask, a nasalcannula, or an inhaler.

In still another aspect, the present disclosure provides an apparatusfor generating nitric oxide to be integrated into a respiratory systemhaving a breathing apparatus and an inspiratory line. The apparatusincludes a chamber having a chamber inlet and at least one or more pairsof electrodes arranged within the chamber, a main chamber configured toprovide a fluid path to an airway of a patient. The apparatus furtherincludes a filter arranged downstream of the electrodes, a scavengerarranged downstream of the electrodes, and one or more sensorsconfigured to measure at least one of an oxygen concentration upstreamof the electrodes, a barometric pressure, a nitric oxide concentrationdownstream of the scavenger, and a nitrogen dioxide concentrationdownstream of the scavenger. The apparatus further includes a controllerin communication with the electrodes and the one or more sensors. Thecontroller is configured to supply an electrical signal to theelectrodes that controls timing and sparking characteristics of theelectrodes. The chamber is in communication with the main chamber andgas in the chamber is non-mechanically introduced into the main chamber.

In some embodiments, the main chamber includes a venturi.

In some embodiments, the apparatus further comprises a passageconnecting the chamber to the venturi of the main chamber.

In some embodiments, a flow of gas through the venturi is configured todraw a vacuum on the chamber.

In some embodiments, the apparatus further comprises a pre-scavengerarranged upstream of the chamber inlet.

In some embodiments, the apparatus further comprises a pre-filterarranged upstream of the chamber inlet.

In some embodiments, the main chamber and the chamber define a parallelpath.

In yet another aspect, the present disclosure provides a method ofgenerating nitric oxide in a respiratory system having a breathingapparatus in communication with an airway of a patient. The methodincludes coupling an nitric oxide generator having a pair of electrodesto the airway of the patient, triggering the nitric oxide generator toproduce a desired concentration of nitric oxide gas, and determiningdesired sparking characteristics of the electrodes to produce thedesired concentration of nitric oxide gas. The method further includesonce the sparking characteristics have determined, supplying anelectrical signal to the electrodes that initiates the desired sparkingcharacteristics between the electrodes to generate the desiredconcentration of nitric oxide gas in a flow of gas provided to theairway of the patient.

In some embodiments, triggering the nitric oxide generator to produce adesired concentration of nitric oxide gas comprises monitoring at leastone of a gas flowrate provided to the patient, a temperature of gasprovided to the patient, and a pressure of gas provided to the patient,detecting a change in at least one of the gas flowrate provided to thepatient, the temperature of gas provided to the patient, and thepressure of gas provided to the patient, and determining that the changedetected is indicative of an inspiratory event.

In some embodiments, the method further comprises filtering particulatesin the flow of gas provided to the patient.

In some embodiments, the method further comprises scavenging at leastone of nitrogen dioxide and ozone in the flow of gas provided to thepatient.

In some embodiments, determining desired sparking characteristics of theelectrodes comprises measuring an atmospheric pressure, and determininga number of electrode spark groups per second, a number of individualelectrode sparks per spark group, a time between individual electrodesparks, and a pulse duration.

In some embodiments, the method further comprises monitoring a nitricoxide concentration downstream of the electrodes, determining that thenitric oxide concentration is not equal to the desired concentration ofnitric oxide, and in response to determining that the nitric oxideconcentration downstream of the electrodes is not equal to the desirednitric oxide concentration, varying via the electrical signal, at leastone of a number of electrode spark groups per second, a number ofindividual electrode sparks per spark group, a time between individualelectrode sparks, and a pulse duration.

In some embodiments, the method further comprises monitoring a nitrogendioxide concentration downstream of the electrodes, determining that thenitrogen dioxide concentration is greater than a pre-defined maximumconcentration, and upon determining that the nitrogen dioxideconcentration downstream of the electrodes is greater than thepre-defined maximum concentration, ceasing the supplying of theelectrical signal to the electrodes.

The foregoing and other aspects and advantages of the invention willappear from the following description. In the description, reference ismade to the accompanying drawings which form a part hereof, and in whichthere is shown by way of illustration a preferred embodiment of theinvention. Such embodiment does not necessarily represent the full scopeof the invention, however, and reference is made therefore to the claimsand herein for interpreting the scope of the invention.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be better understood and features, aspects andadvantages other than those set forth above will become apparent whenconsideration is given to the following detailed description thereof.Such detailed description makes reference to the following drawings.

FIG. 1 shows a schematic illustration of a respiratory system accordingto one embodiment of the present invention.

FIG. 2 shows a detailed schematic of a nitric oxide generator in therespiratory system of FIG. 1 according to one embodiment of the presentdisclosure.

FIG. 3 shows an electrical signal applied to electrodes of the nitricoxide generator of FIG. 2 according to one embodiment of the presentdisclosure.

FIG. 4 shows a schematic illustration of a respiratory system accordingto another embodiment of the present invention.

FIG. 5 shows a detailed schematic of a nitric oxide generator in therespiratory system of FIG. 4 according to another embodiment of thepresent disclosure.

FIG. 6 shows one implementation of the nitric oxide generator of FIG. 5according to one embodiment of the present disclosure.

FIG. 7 shows a respiratory system according to yet another embodiment ofthe present disclosure.

FIG. 8 shows a respiratory system according to still another embodimentof the present disclosure.

FIG. 9 shows a schematic used for testing a nitric oxide generatoraccording to one embodiment of the present disclosure.

FIG. 10 shows a graph illustrating concentrations of NO and NO₂generated while testing the nitric oxide generator of FIG. 2.

FIG. 11. shows a graph illustrating NO and NO₂ concentrations generatedby the nitric oxide generator of FIG. 2 over the 10 day test.

FIG. 12 shows a graph illustrating the effect of varying the electricalsignal to the electrodes of the nitric oxide generator of FIG. 2.

FIG. 13 shows a graph illustrating NO and NO₂ concentrations generatedby the nitric oxide generator of FIG. 2 at varying atmosphericpressures.

FIG. 14 shows a graph illustrating the NO and NO₂ concentrationsentering and exiting a scavenger following and in series with the nitricoxide generator of FIG. 2.

FIG. 15 shows a graph illustrating the NO and NO₂ concentrationsentering and exiting a scavenger of the nitric oxide generator of FIG.5.

FIG. 16 shows a graph illustrating the ozone (O₃) concentrationsentering and exiting a scavenger of the nitric oxide generator of FIG.2.

FIG. 17A shows a magnified view of an unused electrode tip.

FIG. 17B shows a magnified view of the electrode tip of FIG. 17A aftercontinuous sparking for 10 days.

FIG. 18A shows a magnified view of an unused filter.

FIG. 18B shows a magnified view of the filter of FIG. 18A after beingarranged downstream of electrodes continuously sparking for 10 days.

FIG. 19A shows a graph illustrating the energy-dispersive X-ray (EDX)spectroscopy results of the filter of FIG. 18A

FIG. 19B shows a graph illustrating the energy-dispersive X-ray (EDX)spectroscopy results of the filter of FIG. 18B.

FIG. 20 shows a graph illustrating the NO₂/NO ratio generated byelectrodes fabricated from various metals.

FIG. 21 shows a graph illustrating the NO and NO₂ concentrationsgenerated with and without a microporous membrane covering the nitricoxide generator of FIG. 5.

FIG. 22A shows a graph illustrating the mean pulmonary artery pressure(PAP) of an anesthetized lamb with acute pulmonary hypertension due toU46619 infusion following inhalation of nitric oxide generated using therespiratory system of FIG. 1 and compared with nitric oxide deliveredfrom a compressed NO/N₂ gas cylinder.

FIG. 22B shows a graph illustrating the pulmonary vascular resistanceindex (PVRI) of an anesthetized lamb with acute pulmonary hypertensionfollowing inhalation of nitric oxide generated using the respiratorysystem of FIG. 1 and compared with nitric oxide delivered from acompressed NO/N₂ gas cylinder.

FIG. 23A shows a graph illustrating the mean pulmonary artery pressure(PAP) of an anesthetized lamb with acute pulmonary hypertensionfollowing inhalation of nitric oxide generated using the respiratorysystem of FIG. 4 with the nitric oxide generator continuously sparkingand compared with nitric oxide delivered from a compressed gas cylinder.

FIG. 23B shows a graph illustrating the pulmonary vascular resistanceindex (PVRI) of an anesthetized lamb with acute pulmonary hypertensionfollowing inhalation of nitric oxide generated using the respiratorysystem of FIG. 4 with the nitric oxide generator continuously sparkingand compared with nitric oxide delivered from a compressed gas cylinder.

FIG. 24A shows a graph illustrating the mean pulmonary artery pressure(PAP) of an anesthetized lamb with acute pulmonary hypertensionfollowing inhalation of nitric oxide generated using the respiratorysystem of FIG. 4 with the nitric oxide generator intermittently sparkingand compared with nitric oxide delivered from a compressed gas cylinder.

FIG. 24B shows a graph illustrating the pulmonary vascular resistanceindex (PVRI) of an anesthetized lamb with acute pulmonary hypertensionfollowing inhalation of nitric oxide generated using the respiratorysystem of FIG. 2 with the nitric oxide generator intermittently sparkingand compared with nitric oxide delivered from a compressed gas cylinder.

DETAILED DESCRIPTION

The use of the terms “downstream” and “upstream” herein are terms thatindicate direction relative to the flow of a gas. The term “downstream”corresponds to the direction of gas flow, while the term “upstream”refers to the direction opposite or against the direction of gas flow.

Currently, administration of inhaled nitric oxide (NO) therapy requiresthe use of heavy compressed gas cylinders, a gas cylinder distributionnetwork, a complex delivery device, gas monitoring and calibrationdevices, and trained respiratory therapy staff. These requirements foradministering NO therapy present a significant cost to the institution(e.g., a hospital) administering the NO therapy and, therefore, to thepatient receiving the NO therapy. For many institutions, inhaled NOtherapy can be one of the most expensive drugs used in neonatalmedicine. The use of bulky gas cylinders and the expense of inhaled NOtherapy result in inhaled NO therapy not being available in most of theworld and it is not available for outpatient use.

Several methods have been attempted to produce NO for biomedicalpurposes, such as, chemically preparing NO from N₂O₄ requiring extensivescavenging with antioxidants. Various electrical systems have also beenattempted, such as, pulsed arc, gliding arc, dielectric barrier,microwave, corona, radio frequency induced coupled discharge, andnon-thermal atmospheric pressure high-frequency plasma discharge.However, these systems and methods produce large amounts of harmfulbyproducts (e.g., nitrogen dioxide (NO₂) and ozone (O₃)) and requirecomplex purification systems.

Due to the current difficulties in administering and generating NO forinhalation therapy, it would be desirable to have a lightweight andeconomical NO generator that can be used for NO inhalation therapy atthe bedside of a patient or in portable applications. It would also bedesirable to have the NO generator be easily coupled to or integratedinto current ventilator systems. It is advantageous from a safetyperspective to have the NO that is generated be as clean as possible, sothat even in the event that a scavenger fails or is exhausted, the NOthat is delivered to a patient is not contaminated with NO₂ or O₃

FIG. 1 shows a respiratory system 10 for administering NO to a patient11 according to one non-limiting example of the present disclosure. Therespiratory system 10 includes a breathing apparatus 12 and a NOgenerator 14. In some non-limiting examples, the breathing apparatus 12can be a ventilator system, a continuous positive airway pressure (CPAP)system, a High Frequency Oscillatory Ventilator (HFOV), a face mask, anasal cannula or an inhaler. The breathing apparatus 12 is configured toenable the passage of gas to and from an airway of the patient 11. Insome non-limiting examples, the breathing system 12 can providemechanical ventilation (i.e., positive pressure to inflate the patient's11 lungs) to the patient. In other non-limiting examples, the patient 11may be breathing on their own and the breathing system 12 can provide aflow path to the airway of the patient 11. The illustrated breathingsystem 12 includes an inspiratory line 18, an expiratory line 20, and anairway flowmeter 22 coupled to the inspiratory line 18. The ventilator16 can be a commercially available mechanical ventilator used inbiomedical applications (e.g., inhalation therapy). As is known in theart, the mechanical ventilator 16 is configured to provide a flow of gas(e.g., air or a nitrogen/oxygen gas mixture) via the inspiratory line 18to the respiratory tract of the patient 11. Subsequently, the ventilator16 is configured to remove a flow of gas (e.g., exhaled gas) via theexpiratory line 20 from the respiratory tract of the patient 11. In thisway, the ventilator 16 can simulate the breathing process for thepatient 11. The airway flowmeter 22 measures the flowrate of gas in theinspiratory line 18. In one non-limiting example, the airway flowmeter22 may control a timing and amount of NO that is synthesized from sparkplasma discharge in the NO generator 14.

The NO generator 14 is arranged between an inlet 24 and an outlet 26.Gas (e.g., air or a nitrogen/oxygen gas mixture) is drawn into the NOgenerator 14 at the inlet 24. The NO generator 14 is configured togenerate a predetermined concentration of NO to be inhaled by thepatient 11, as will be described in detail below. The NO containing gasis furnished from the NO generator 14 to the outlet 26. The outlet 26communicates with the inspiratory line 18 of the breathing apparatus 12upstream of the airway flowmeter 22.

The respiratory system 10 includes a pre-filter 28, a gas pump 30, a gasflow sensor 32 all arranged upstream of the NO generator 14. Thepre-filter 28 is arranged downstream of the inlet 24 and upstream of thegas pump 30. The gas flow sensor 32 is arranged downstream of the gaspump 30 and upstream of the NO generator 14. In one non-limitingexample, the pre-filter 28 can be configured to filter particles, waterdroplets and bacteria with a diameter larger than approximately 0.22micrometers (μm). It should be known that the particle size filtered bythe pre-filter 28 is not meant to be limiting in any way, andalternative pre-filters that filter different particle sizes are withinthe scope of the present disclosure. In other non-limiting examples, thepre-filter 28 may be removed if the fluid provided at the inlet 24 is bepre-treated (i.e., filtered and dried). In some embodiments, apre-scavenger (not shown) can be arranged upstream of the pre-filter 28to remove, for example, CO₂ from the inlet gas. Removing CO₂ from theinlet gas negates the need for the scavenging CO₂ in the gas output fromthe NO generator 14.

The gas pump 30 is configured to draw gas from inlet 24 and furnish thegas under an increased pressure towards NO generator 14 and through theoutlet 26. It should be known that, in other non-limiting examples, thegas pump 30 can be replaced by a fan or a bellows type device. The gasflow sensor 32 is configured to measure a flowrate of gas flowing fromthe gas pump 30 to the NO generator 14. A controller 33 is incommunication with the NO generator 14, the gas pump 30, the gas flowsensor 32 and the airway flowmeter 22. The controller 33 is configuredto control the operation of the NO generator 14 and the gas pump 30, aswill be described in detail below.

As shown in FIG. 2, the NO generator 14 includes an oxygen sensor 34arranged upstream of electrodes 36. The oxygen sensor 34 measures anoxygen concentration in the gas being supplied, via the gas pump 30, tothe electrodes 36. In some non-limiting examples, the electrodes 36 caninclude one or more pairs of individual electrodes that can befabricated from or plated with tungsten carbide, carbon, nickel,iridium, titanium, platinum, rhenium, or an alloy of the aforementionedmaterials. In one exemplary non-limiting example, the electrodes 36 arefabricated from or plated with iridium because, as described below,iridium can produce a lower concentration of NO₂ relative to theconcentration of NO generated which is an important safety factor of theNO generator 14.

An ignition coil 38 is in communication with the electrodes 36 and isconfigured to store and release electrical energy. The energy stored bythe ignition coil 38 is delivered to the electrodes 36 to create aplasma in a gap between the electrodes 36. The plasma generated betweenthe electrodes 36 generates NO, as long as nitrogen and oxygen arepresent in the gas being supplied to the electrodes 36. The controller33 is in communication with the ignition coil 38 and is configured tocontrol when the ignition coil 38 delivers the stored energy and,therefore, control when the electrodes 36 spark (i.e., form a plasma andgenerate NO). It should be known that, in some non-limiting examples,the controller 33 can be combined with the NO generator 14 into asingle, portable unit.

Downstream of the electrodes 36, the NO generator 14 includes ascavenger 42, a post-filter 44, a NO sensor 46, and a NO₂ sensor 48. Thepost-filter 44 is arranged upstream of the NO and NO₂ sensors 46 and 48,and downstream of the scavenger 42. The scavenger 42 is configured toremove harmful byproducts (e.g., NO₂ and O₃) produced in the plasmacreated by sparking the electrodes 36. In one non-limiting example, thescavenger 42 can be fabricated from calcium hydroxide (Ca(OH)₂). Thepost-filter 44 is configured to filter particles (e.g., fragments fromthe scavenger 42 and/or particles that break off from the electrodes 36during sparking) in the fluid flowing from the electrodes 36 to theoutlet 26. This can prevent the patient 11 from inhaling particle-ladengas and from inhaling electrode particles that boil off due to hightemperatures during sparking. In one non-limiting example, thepost-filter 44 can be configured to filter particles with a diameterlarger or smaller than approximately 0.22 μm. It should be known thatthe particle size filtered by the post-filter 44 is not meant to belimiting in any way, and alternative post-filters that filter differentparticle sizes are within the scope of the present disclosure. However,the particle size filtered by the post-filter 44 should be sufficientlysmall to maintain the safety and health of the patient 11.

The NO sensor 46 measures a concentration of NO in the gas flowing fromthe electrodes 36 to the outlet 26, and the NO₂ sensor 48 measures aconcentration of NO₂ in the fluid flowing from the electrodes 36 to theoutlet 26.

With continued reference to FIG. 2, the controller 33 receives inputpower from a power supply 50. In one non-limiting example, the powersupply 50 can be external to the NO generator 14 (e.g., wall power). Inanother non-limiting example, the power supply 50 can be integrated intothe NO generator 14. In this non-limiting example, the power supply 50can be in the form of a battery or a rechargeable battery. Thecontroller 33 includes a transceiver 52 and a communication port 54. Thecontroller 33 can be configured to communicate wirelessly, via thetransceiver 52, with an external processor (not shown) and/or a display(not shown) using Bluetooth®, WiFi, or any wireless communicationprotocol known in the art or developed in the future. Alternatively oradditionally, the controller 33 can be configured to communicate, viathe communication port 54, with the external processor (not shown)and/or the display (not shown) using a universal serial bus (USB)connection, an Ethernet connection, or any wired communication protocolknown in the art or developed in the future.

The controller 33 is in communication with the gas pump 30, the gas flowsensor 32, the oxygen sensor 34, the NO sensor 46 and the NO₂ sensor 48.In operation, the controller 33 is configured to control a displacement(i.e., a flowrate of gas from the inlet 24 to the outlet 26) of the gaspump 30. For example, a desired flowrate of 5 liters/minute (L/min) canbe input to the controller 33 by the external processor. In thisnon-limiting example, the controller 33 can adjust the displacement ofthe gas pump 30 in response to the flowrate measured by the gas flowsensor 32 to attempt to maintain the flowrate within a predefined marginof approximately 5 L/min.

The concentrations measured by the oxygen sensor 34, the NO sensor 46,and the NO₂ sensor 48 are communicated to the controller 33. Inoperation, the controller 33 is configured to vary the timing and thesparking characteristics of the electrodes 36 in response to themeasurements of the oxygen sensor 34, the NO sensor 46 and the NO₂sensor 48 and the airway flowmeter 22. In one non-limiting example, thetiming of the electrodes 36 can be with respect to inspiration of thepatient 11. As shown in FIG. 3, the controller 33 is configured supplyan electrical signal to the ignition coil 38 and thereby to theelectrodes 36 that comprises a plurality of square waves. In thenon-limiting example shown in FIG. 3, the electrical signal supplied tothe electrodes 36 by the controller 33 can include groups of squarewaves where each individual square wave in the respective grouprepresents a spark of the electrodes 36. In this non-limiting example,the controller 33 can be configured to control a number spark groups persecond (B), a number of individual sparks per group (N), a time betweenindividual sparks (P), and a pulse duration of each individual squarewave in the group (H).

Varying the values of B, N, P, and H can alter concentrations of NO andNO₂ generated by the NO generator 14, as will be described in detailbelow. The data gathered from varying B, N, P, and H can be used todevelop a theoretical model for generating a given concentration of NO.The theoretical model can be further refined by testing the NO generator14 at different oxygen concentrations, pressures, humidities, andtemperatures. Then, knowing the oxygen concentration, pressure,temperature, and/or humidity of the fluid flowing to the electrodes 36,the controller 33 can calculate an ideal B, N, P, and H to generate adesired concentration of NO. The NO sensor 46 monitors the concentrationof NO produced and provides feedback to the controller 33 which, inresponse to the concentration of NO produced deviating from a desiredconcentration, can alter the values of B, N, P, and/or H accordingly.

In one non-limiting example, the oxygen concentration of the gasprovided to the electrodes 36 may be a constant, known value (e.g., airwith 21% O₂) which is input to the controller 33. In this non-limitingexample, the oxygen sensor 34 may be omitted from the NO generator 14.Alternatively or additionally, a pressure sensor (not shown) can bearranged upstream of the electrodes 36 to measure ambient pressure. Asdescribed below, the amount of NO produced by the NO generator 14 can bea function of atmospheric pressure. In one non-limiting example, thecontroller 33 can be configured to adjust the sparking characteristicsof the electrodes 36 in response to the pressure measured by thepressure sensor. Alternatively or additionally, the controller 33 can beconfigured to monitor a condition, or health, of the scavenger 42 bydetermining if the concentration of NO₂, measured by the NO₂ sensor 48,exceeds a pre-determined value. If the NO₂ concentration exceeds thepre-determined value, the scavenger 42 may be exhausted and thecontroller 33 can cease the sparking of the electrodes 36 and instruct auser of the NO generator 14 to replace the scavenger 42. Alternativelyor additionally, a colorimetric pH sensor can estimate exhaustion of thescavenger 42.

In operation, the NO generator 14 is configured to produce therapeuticconcentrations of NO, for example, between approximately 5 and 80 partsper million (ppm) by pulsed sparking of the electrodes 36. Thetherapeutic concentrations of NO produced by the NO generator 14 can besupplied to the inspiratory line 18 and thereby to the patient 11. Thus,the NO generator 14 does not require the use of valves to enable theflow of NO laden gas to the patient 11. In one non-limiting example, theelectrodes 36 of the NO generator 14 can be triggered, by the controller33, to spark continuously. In another non-limiting example, theelectrodes 36 of the NO generator 14 can be triggered, by the controller33, to spark during or prior to inspiration of the patient 11.Triggering the electrodes 36 during or prior to inspiration can avoidwaste NO generated during exhalation, and can enable the NO generator 14to demand less power when compared with continuous operation.

The controller 33 can be configured to detect inspiration of the patient11 based on the flowrate measured by the airway flowmeter 22, atemperature in the inspiratory line 18, a temperature in the expirationline 20, a pressure in the inspiratory line 18, and/or a pressure in theexpiration line 20. The theoretical model executed by the controller 33for determining the values of B, N, P, and H for a desired NOconcentration can be adjusted whether the electrodes 36 are beingsparked continuously or intermittently (i.e., triggered during or priorto inspiration).

FIG. 4 shows a schematic illustration of a respiratory system 100according to another non-limiting example of the present disclosure. Therespiratory system 100 of FIG. 4 is similar to the respiratory system 10of FIG. 1 except as described below or is apparent from FIG. 4. As shownin FIG. 4, the respiratory system 100 includes a NO generator 102integrated into the inspiratory line 18 of the breathing apparatus 12.With the NO generator 102 integrated into the inspiratory line 18, therespiratory system 100 may not include the pre-filter 28, the gas pump30, and the gas flow sensor 32, as the ventilator 16 provides the flowof gas to the NO generator 102.

The NO generator 102 of FIG. 5 is similar to the NO generator 14 of FIG.1 except as described below or is apparent from FIG. 5. As shown in FIG.5, the scavenger 42, the post-filter 44, the NO sensor 46 and the NO₂sensor are integrated into the inspiratory line 18, and the NO generator102 includes a membrane 104 surrounding or covering the electrodes 36.The membrane 104 protects the electrodes 36 from any water droplets ormucous in the inspiratory line 18 while allowing the gas flowing throughthe inspiratory line 18 (e.g., air or a nitrogen/oxygen gas mixture) tofreely pass through the membrane 104. In one non-limiting example, themembrane 104 can be a microporous polytetrafluoroethylene (PTFE)membrane. It should be known that the electrodes 36 do not need becompletely integrated into the inspiratory line 18, and that only thetips of the electrodes 36 need to be in the gas path defined by theinspiratory line 18.

In operation, placing the NO generator 102 inline with the inspiratoryline 18 reduces the transit time of the generated NO gas to the lung ofthe patient 11. This reduces the probability of the generated NOoxidizing to NO₂ prior to reaching the patient 11. Also, placing the NOgenerator 102 inline with the inspiratory line 18 negates the need forvalves to enable the flow of NO laden gas to the patient 11. In onenon-limiting example, the controller 33 is configured to intermittentlyspark the electrodes 36 of the NO generator 102 prior to or duringinspiration of the patient 11. Generating NO only during or uponinspiration, compared to continuous sparking of the electrodes 36,enables the NO generator 102 to generate NO during approximately onequarter to one eighth of the total respiratory cycle time of the patient11. This can reduce the power demanded of the NO generator 102, favorportable applications, avoid generating waste NO, and reduce a necessarysize of the scavenger 42.

FIG. 6 shows one non-limiting implementation of the NO generator 102where the controller 33 and the ignition coil 38 are enclosed in a base110. The base 110 is coupled to a tube 112 configured to be placedinline with an inspiratory line of a respiratory system, or breathingapparatus. The electrodes 36 are arranged partially within the base 110such that the tips of the electrodes 36 are in a fluid path defined bythe tube 112. The illustrated NO generator 102 includes a power cord 114attached to the base 102 to supply power to the controller 33 and thepower supply 50. The power cord 114 is detachable from the base 110 toaid in the portability of the NO generator 102.

A first end 116 of the tube 112 is configured to receive a cartridgeassembly 118 and a second end 117 of the tube 112 is configured tocouple to the inspiratory line 18. The cartridge assembly 118 includes acartridge inlet 119 configured to couple to the first end 116 of thetube 112, a cartridge 120 arranged upstream of and coupled to thepost-filter 44, and a cartridge outlet 122 configured to couple to theinspiratory line 18. In one non-limiting example, the cartridge 120 canbe filled with a microporous material (e.g., foam). The scavenger 42 isarranged between the cartridge 120 and the post-filter 44.

FIG. 7 shows a respiratory system 200 having an NO generator 201according to another non-limiting example of the present disclosure. Asshown in FIG. 7, the NO generator 201 includes a chamber 202 having achamber inlet 204 arranged upstream of electrodes 206. Similar to theelectrodes 36, described above, the electrodes 206 can be powered by acontroller 207 which is configured to control when energy is deliveredto the electrodes 206 and, therefore, control when the electrodes 206spark (i.e., form a plasma and generate NO). The chamber 202 is coupledto a main chamber 208 via passage 210. The main chamber 208 includes amain inlet 212, a main outlet 214 and a venturi 216 arrangedtherebetween. The main outlet 214 is in gas communication with therespiratory tract of a patient. The passage 210 is coupled to theventuri 216 of the main chamber 208 and includes a post-filter 218 and apost-scavenger 220. The post-filter 218 is configured to filterparticles (e.g., particles that break off or are vaporized from theelectrodes 36 during sparking) in the gas flowing through the passage210 from the chamber 202 to the main chamber 208. The post-scavenger 220is configured to remove harmful byproducts (e.g., NO₂ and O₃) producedin the plasma created by sparking the electrodes 206. In othernon-limiting examples, the post-filter 218 and/or the post-scavenger 220may be arranged in the main chamber 208 downstream of the venturi 216.

In one non-limiting example, a pre-filter 222 may be arranged upstreamof the chamber inlet 202 to remove particles and/or water droplets inthe fluid being supplied to the chamber inlet 202. Alternatively oradditionally, a pre-scavenger 224 may be arranged upstream of thechamber inlet 202 to remove compounds which are potentially harmful tothe post-scavenger 220 (e.g., carbon dioxide (CO₂)). Pre-scavenging thegas flowing to the electrodes 206 can enable a size of thepost-scavenger (not the post-filter) 220 to be reduced. Reducing thesize of the post-scavenger 220 by pre-scavenging can, in onenon-limiting example, enable the post-scavenger 220 to be placed over aspark gap between the electrodes 206 within a tracheostomy tube or anendotracheal tube to produce NO within the airway, even close to thecarina.

One or more sensors 226 are arranged downstream of the venturi 216. Thesensors 226 are configured to measure an oxygen concentration, a NOconcentration, and/or an NO₂ concentration in the gas flowing from theventuri 216 to the main outlet 214. Alternatively or additionally, thechamber 202 may include one or more additional sensors (not shown) tomeasure at least one of a pressure, a temperature, and a humidity in thechamber 202.

In some non-limiting examples, the main chamber 208, the chamber 202,and/or the passage 210 may include one or more other passages ormodules, such as a ventilator gas stream or breathing apparatus.

In operation, the main inlet 212 and the chamber inlet 204 receive aflow of gas (e.g., air or a nitrogen/oxygen gas mixture). The flowrateof gas provided to the main inlet 212 can be sufficiently greater thanthe flowrate of gas provided to the chamber inlet 204 which causes theflow through the venturi 216 to draw a vacuum on the chamber 202. Thevacuum drawn on the chamber 202 can draw fluid from the chamber 202 intothe main chamber 208. This operation of the NO generator 201 can obviatethe need to control the total amount of NO rich gas injected into themain chamber 208 with one or more valves. Also, the NO generator 201non-mechanically, (i.e., without the use of a pump or valves) providesthe flow of NO laden gas to the patient.

The operation of the controller 207 is similar to the controller 33,described above, and is configured to control the concentration of NOgenerated by sparking the electrodes 206 by varying B, N, P, and H. Thecontroller 207 can adjust B, N, P, and/or H in response to themeasurements by the one or more sensors 226. In one non-limitingexample, the desired concentration of NO generated for a particularapplication can be calculated by the controller 207 based on the massflowrate of gas through the main chamber 208 and the amount of vacuumdrawn on the chamber 202. In some non-limiting examples, the NOgenerator 201 can include a flow sensor (not shown) in communicationwith the controller 207 to enable timed inspiratory generation of NO. Inthis non-limiting example, the controller 207 can be configured totrigger the electrodes 206 to generate NO during or prior to inspirationof the patient which can reduce wear of the electrodes 206, oxidation ofNO into NO₂, and the power requirements of the NO generator 201.

FIG. 8 shows a respiratory system 300 having a NO generator 301according to another non-limiting example of the present disclosure. TheNO generator 301 of FIG. 8 is similar to the NO generator 201 of FIG. 7except as described below or is apparent from FIG. 8. As shown in FIG.8, the NO generator 301 can employ a proportional parallel delivery.Rather than mixing the gas before it is delivered to the patient, aninspiration can pull NO rich gas from the chamber 202 and fluid from themain chamber 208 from a parallel passage 302. That is, the patient candraw output gas directly from the parallel passage 302 without requiringthe use of valves or a pump to furnish the produced NO laden gas to thepatient.

As described above, the NO generators 14, 102, 201, and 301 may operatesimilarly to provide safe and pure NO to a patient's airway. Theoperation of the respective controller (i.e., controllers 33 and 207) inthe respiratory systems 10, 100, 200, and 300 can control the operationof the NO generators 14, 102, 201, and 301. FIG. 9 shows onenon-limiting example of the operation of any of the above-describedrespiratory systems 10, 100, 200, and 300. As shown in FIG. 9, a NOgenerator (e.g., NO generator 14, 102, 201, and/or 301) is coupled to anairway of a patient at step 304. As described above, the NO generatorcan be coupled to the airway of the patient, for example via aconnection to an inspiration line, a venturi, a parallel path, or the NOgenerator can be placed inline with an airway of the patient. With theNO generator coupled to the airway of the patient, the controller (e.g.,controller 33 or controller 207) monitors sensor inputs to the patientat step 306. In some non-limiting examples, the controller can monitoran oxygen concentration downstream of the NO generator, an ambientpressure, a gas flowrate being provided (mechanically ornon-mechanically) to the patient, a NO concentration downstream of theNO generator, and a NO₂ concentration downstream of the NO generator.

The controller (e.g., controller 33 or controller 207) then determinesat step 308 if the NO generator should be triggered to produce NO to beinhaled by the patient. In some non-limiting examples, the controllercan be configured to trigger at or just before an inspiratory event(e.g., by monitoring the gas flow provided to the patient, a pressure inan inspiratory line, a temperatures in an inspiratory line, etc.). Inother non-limiting examples, the controller can be manually triggered bya user of the NO generator. Once the NO generator has been triggered bythe controller at step 308, the controller can determine the desiredsparking characteristics, provided by a pulsed electrical signal, to besent to electrodes (e.g., electrodes 36 or electrodes 208) at step 310.The controller can be pre-configured to produce a desired concentrationof pure and safe NO gas to be inhaled by the patient. In onenon-limiting example, the pre-configured concentration of NO gas isdetermined at step 310 by the controller as a function of theatmospheric pressure and/or the B, N, P, and H electrode sparkcharacteristics, described above. That is, the controller can, based onthe measured atmospheric pressure, determine the desired B, N, P, and Hof the electrical signal to produce the pre-configured concentration ofNO.

With the desired sparking characteristics determined at step 310, thecontroller sends the corresponding electrical signal to the electrodesand the NO generator produces, at step 312, the pre-configuredconcentration on pure and safe NO gas by spark plasma discharge to beprovided to the airway of the patient. While the NO generator isproducing NO gas at step 312, the controller monitors the inputs fromthe sensors (e.g., an oxygen concentration upstream of the NO generator,an ambient pressure, a gas flowrate being provided (mechanically ornon-mechanically) to the patient, a NO concentration downstream of theNO generator, and a NO₂ concentration downstream of the NO generator.Based on the inputs from the sensors, the controller determines at step314 whether or not to adjust the NO production. For example, ifcontroller detects that the output NO gas concentration is notsubstantially equal to the desired NO gas concentration, the controllercan alter the sparking characteristics of the electrodes, at step 316,by varying at least one of B, N, P, and H to bring the produced NO gasconcentration in line with the desired NO gas concentration.Alternatively or additionally, if the controller detects an increase ingas flow being provided to the airway of the patient, the controller canalter the sparking characteristics of the electrodes, at step 316 byvarying at least one of B, N, P, and H accordingly. Thus, the controller(e.g., controller 33 or controller 207) is configured to alter thesparking characteristics (i.e., a concentration of synthesized NO gasproduced by spark plasma discharge between the electrodes) based on thefeedback from one or more sensors.

EXAMPLES

The following examples set forth, in detail, ways in which therespiratory systems 100 and 200 and/or the NO generators 14, 102, 201and 301 may be used or implemented, and will enable one of skill in theart to more readily understand the principle thereof. The followingexamples are presented by way of illustration and are not meant to belimiting in any way.

Example 1: Measuring NO and NO₂ Generation at Varying Oxygen andNitrogen Concentrations

The NO generator 14 was tested with varying nitrogen and oxygenconcentrations being provided to the electrodes 36. The test wasperformed using the test setup shown in FIG. 9 and at atmosphericpressure. The controller 33 was configured to spark the electrodes 36using the following settings: B=25; N=35; P=240 μs; and H=100 μs. The NOand NO₂ concentrations generated by the NO generator 14 were measured ata constant gas flow of 5 L/min and with oxygen levels of 10%, 21%, 50%,80%, and 90% and a balanced amount of nitrogen. FIG. 10 shows theconcentrations of NO and NO₂ generated during the test. As shown in FIG.10, maximum NO (68±4 ppm) and NO₂ (6±2 ppm) concentrations weregenerated at 50% oxygen. Lower concentrations of NO and NO₂ weregenerated as the oxygen concentration deviated from 50% (i.e., eitherincreasing the oxygen concentration above 50% or decreasing the oxygenconcentration below 50%).

Example 2: Measuring the NO and NO₂ Concentrations During ContinuousOperation for 10 Days

The NO generator 14 was tested at an oxygen concentration of 21% (i.e.,in air) and a constant gas flow rate of 5 L/min. The electrodes 36 werefabricated from iridium-platinum. The test was performed using the testsetup shown in FIG. 9 and at atmospheric pressure. The controller 33 wasconfigured to spark the electrodes 36 using the following settings toproduce approximately 50 ppm of NO: B=20, N=20, P=240 μs; and H=70 μs.FIG. 11 shows the NO and NO₂ concentrations generated by the NOgenerator over the 10 day test. As shown in FIG. 11, the NO and NO₂concentrations remained substantially constant over the 10 days.

Example 3: Measuring NO and NO₂ Generation at Varying B, N, P, and H

As described above, a theoretical model of the NO and NO₂ generation atvarying B, N, P, and H, can be input to the controller of the respectiverespiratory system. The NO generator 14 was tested at an oxygenconcentration of 21% (i.e., in air) and a constant gas flow rate of 5L/min. The electrodes were fabricated from iridium-platinum. The testwas performed using the test setup shown in FIG. 9 and at atmosphericpressure. FIG. 12A shows the effect of varying B with N=25, P=240 μs,and H=100 μs. As shown in FIG. 12A, the NO and NO₂ concentrationsgenerated increased substantially and linearly with increasing values ofB. FIG. 12B shows the effect of varying N with B=35, P=240 μs, and H=100μs. As shown in FIG. 12A, the NO and NO₂ concentrations generatedincreased substantially and linearly with increasing values of N. FIG.12C shows the effect of varying P with B=35, N=25, and H=100 μs. Asshown in FIG. 12C, the NO and NO₂ concentrations generated increasedsubstantially and linearly with increasing values of P. FIG. 12D showsthe effect of varying H with B=35, N=25, and P=240 μs. As shown in FIG.12D, the NO and NO₂ concentration generated increased substantially andlinearly with increasing values of H. The data shown in FIGS. 12A-Dindicate that NO production can be precisely controlled (using B, N, P,and H), and that NO production can increase with pulse repetition (B andN) and energy storage capacitance (P and H).

Example 4: Measuring NO and NO₂ Generation at Varying AtmosphericPressure

The NO generator 14 was tested at an oxygen concentration of 21% (i.e.,in air) in a 500 milliliter chamber. The controller 33 was configured tospark the electrodes 36 using the following settings: B=100, N=10, P=140μs; and H=10 μs. The NO generator was run for 1 minute and the NO andNO₂ concentrations were measured at one-third atmospheres absolutepressure (ATA), one-half ATA, one ATA, and two ATA. FIG. 13 shows the NOand NO₂ concentrations at the varying atmospheric pressures. As shown inFIG. 13, compared to NO and NO₂ concentrations generated at one ATA, theNO and NO₂ production decreased with decreasing ATA and increased withincreasing ATA. However, the ration of NO₂/NO remained substantiallyconstant for each of the atmospheric pressures tested.

Example 5: Measuring NO and NO₂ Concentrations Entering and Exiting theScavenger 42 of the NO Generator 14 at Varying Oxygen and NitrogenConcentrations

The NO generator 14 was tested at a constant gas flow rate of 5 L/min.The electrodes 36 were fabricated from iridium-platinum. The test wasperformed using the test setup shown in FIG. 9 at atmospheric pressure.The scavenger 42 comprised 72 grams (g) of Ca(OH)₂ and the post-filter44 was placed downstream of the scavenger 42. The controller 33 wasconfigured to spark the electrodes 36 using the following settings:B=25, N=35, P=240 μs; and H=100 μs. The NO and NO₂ concentrationsgenerated by the NO generator 14 were measured entering (i.e., upstream)and exiting (i.e., downstream) of the scavenger 42 at oxygen levels of21% (i.e., air), 50%, and 80%, and a balanced amount of nitrogen. FIG.14 shows the concentrations of NO and NO₂ measured during the test. Asshown in FIG. 14, at 21% oxygen (i.e., in air), the NO generator 14produced 48±5 ppm NO and 44±5 ppm exited the scavenger 42. The NOgenerator 14 produced 4.1±0.4 ppm NO₂ and 0.5±0.03 ppm exited thescavenger 42. At 50% oxygen, the NO generator 14 produced 68±11 ppm NOand 62±11 ppm exited the scavenger 42. The NO generator 14 produced6.2±0.4 ppm NO₂ and 0.7±0.02 ppm exited the scavenger 42. At 80% oxygen,the NO generator 14 produced 41±1 ppm NO and 37±2 ppm exited thescavenger 42. The NO generator 14 produced 3.9±0.5 ppm NO₂ and 0.9±0.04ppm exited the scavenger 42. Thus, the scavenger 42 removed betweenapproximately 87% and 95% of the NO₂ produced by the NO generator 14.These results demonstrate that the scavenger 42 is highly efficient atremoving NO₂ (to below the Environmental Protection Agency (EPA) limitafter scavenging) without reducing the NO concentrations.

Example 6: Measuring NO and NO₂ Concentrations Entering and Exiting theScavenger 42 of the NO Generator 102

As described above, the NO generator 102 is similar to the NO generator14 but is arranged inline on the inspiratory line 18, upstream ofexhaled CO₂, which enables the scavenger 42 to be of a reduced size. TheNO generator 102 was tested at a constant gas flow rate of 5 L/min. Thetest was performed using the test setup shown in FIG. 9 at atmosphericpressure. The electrodes 36 were fabricated from iridium-platinum. Thescavenger 42 comprised 15 g of Ca(OH)₂ and the post-filter 44 was placeddownstream of the scavenger 42. The controller 33 was configured tospark the electrodes 36 using the following settings: B=35, N=25, P=240μs; and H=70 μs. The NO and NO₂ concentrations generated by the NOgenerator 102 were measured entering (i.e., upstream) and exiting (i.e.,downstream) the scavenger 42 at oxygen levels of 21% (i.e., air), 50%,and 80%, and a balanced amount of nitrogen. FIG. 15 shows theconcentrations of NO and NO₂ measured during the test. As shown in FIG.15, the scavenger 42 removed approximately over 95% of the NO₂ producedby the NO generator 102. These results are similar to the larger (75 g)scavenger 42. Thus, the smaller scavenger 42 with less gas flowresistance (e.g., 0.2 cmH20*min*L⁻¹), used in the NO generator 102,efficiently removes NO₂ without reducing the NO concentrations.

Example 7: Measuring and Scavenging O₃ Concentrations Produced by the NOGenerator 14

The NO generator 14 was tested at a constant gas flow rate of 5 L/min.The electrodes 36 were fabricated from iridium-platinum. The test wasperformed using the test setup shown in FIG. 9 and at atmosphericpressure. The scavenger 42 comprised 72 grams (g) of Ca(OH)₂ and thepost-filter 44 was placed downstream of the scavenger 42. The controller33 was configured to spark the electrodes 36 using the followingsettings: B=25, N=35, P=240 μs; and H=100 μs. The O₃ concentrationsgenerated by the NO generator 14 were measured entering (i.e., upstream)and exiting (i.e., downstream) of the scavenger 42 at oxygen levels of21% (i.e., air), 50%, and 80%, and a balanced amount of nitrogen. FIG.16 shows the concentrations of O₃ measured during the test. As shown inFIG. 16, at 21% oxygen (i.e., in air), the NO generator 14 produced 17±2parts per billion (ppb) O₃ and <0.1 ppb exited the scavenger 42. At 50%oxygen, the NO generator 14 produced 18±10 ppb O₃ and <0.1 ppb exitedthe scavenger 42. At 80% oxygen, the NO generator 14 produced 20±1 ppbO₃ and <0.1 ppb exited the scavenger 42. These results demonstrate thatthe scavenger 42 is highly efficient at removing O₃ to negligible levelswell below the EPA O₃ limits. Similar results were achieved when testingof the smaller scavenger 42 of the NO generator 102.

Example 8: Electrode Erosion

As described above, the electrodes can break down and vaporize over timedue to the sparking. FIG. 17A shows a new iridium electrode tip and FIG.17B shows a used iridium electrode tip after ten days of operationproducing 50 ppm NO at 5 L/min gas flowrate. As shown in FIG. 17B, theelectrode tip has degraded and lost material due to the sparking events.Thus, the requirement for the post-filter 44 in the NO generator 14 and102, and the post-filter 218 in the NO generator 201 and 301. As theelectrodes erode and vaporize, the electrode fragments are deposited onthe post-filter 44, 218. To verify that the post-filter 44, 218 catchesthe electrode fragments, a post-filter with a 0.22 μm particle sizecutoff was imaged after the ten days of sparking. FIG. 18A shows a new0.22 μm post-filter and FIG. 18B shows the 0.22 μm post-filter after theten days of operation. As shown in FIG. 18B, the used 0.22 μmpost-filter contains iridium fragments. This was verified byenergy-dispersive X-ray (EDX) spectroscopy as shown in the plots of FIG.19A and FIG. 19B. FIG. 19A shows the EDX spectroscopy of the new 0.22 μmpost-filter and FIG. 19B shows the EDX spectroscopy of the used 0.22 μmpost-filter. As shown in FIGS. 19A and 19B, the used 0.22 μm post-filtercontains iridium while the new 0.22 μm post-filter does not containiridium. Thus, a single 0.22 μm post-filter was sufficient and necessaryto catch electrode fragments produced by electrode erosion.

Example 9: Minimizing NO₂ Generation by Varying Electrode Composition

The NO generator 14 was tested at a constant gas flow rate of 5 L/minwith electrodes 36 fabricated from tungsten carbide, carbon, nickel, andiridium. The test was performed using the test setup shown in FIG. 9 andat atmospheric pressure. The controller 33 was configured to spark theelectrodes 36 using the following settings: B=25, N=35, P=240 μs; andH=50 μs. FIG. 20 shows the ratio of NO₂/NO generated for the differentelectrode compositions. As shown in FIG. 20, the iridium electrodeproduced 4.5±0.1% of NO₂/NO, the nickel electrode produced 6.5±0.1% ofNO₂/NO, the carbon electrode produced 7.8±0.5% of NO₂/NO, and thetungsten carbide electrode generated 12.9±1.9% of NO₂/NO. Obviously, thelower the ratio of NO₂/NO the better and, thus, the iridium electrode isan ideal candidate for the composition of the electrodes 36.

Example 10: Measuring NO and NO₂ Diffusion Rates Through the Membrane104 of the NO Generator 102

As described above, since the NO generator 102 is placed inline with theinspiratory line 18, the microporous membrane 104 can be placed aroundthe electrodes 36 to protect them from droplets of water or airwaysecretions. The NO generator 102 was tested at a constant gas flow rateof 0.5 L/min for 5 minutes while producing NO. The NO and NO₂ producedwas averaged over the 5 minutes and the concentrations with (+) andwithout (−) the membrane 104 were measured. The controller 33 wasconfigured to spark the electrodes 36 using the following two sets ofsettings. Setting #1: B=25, N=35, P=240 μs; and H=30 μs. Setting #2:B=25, N=35, P=240 μs; and H=60 μs. FIG. 21 shows the NO and NO₂concentrations produced during the 5 minutes with (+) and without (−)the membrane 104 at the two different spark settings. As shown in FIG.21, 95±2% of the NO generated without (−) the membrane 104 was generatedwith (+) the membrane 104, and 95±1% of the NO₂ generated without (−)the membrane 104 was generated with (+) the membrane 104. Thus, theaddition of the membrane 104 does not significantly alter the NOproduction characteristics of the NO generator 102.

Animal Studies

Animal studies were approved by the Institutional Animal Care and UseCommittee of Massachusetts General Hospital (Boston, Mass.). Eight lambs(New England Ovis, Dover, N.H.) weighing 32±2 kg were studied. Generalanesthesia was induced with 5% inhaled isoflurane(1-chloro-2,2,2-trifluoroethyldifluromethyl ether, Baxter, Deerfield,Ill.) in oxygen delivered via a mask and then maintained with 1-4%isoflurane in 50% oxygen during surgery. After tracheal intubation, thelambs were instrumented with indwelling carotid artery pulmonary arterycatheters. All hemodynamic measurements were performed in anesthetizedlambs ventilated with a mechanical ventilator (model 7200, PuritanBennett, Pleasanton, Calif.) at a tidal volume of 400 ml/min and rate of1245 breaths/min.

To induce pulmonary hypertension, a potent pulmonary vasoconstrictorU46619 (Cayman Chemical, Ann Arbor, Mich.), the analog of theendoperoxide prostaglandin 112, was infused intravenously at a rate of0.8-0.9 μg/kg/min to increase pulmonary arterial pressure (PAP) to 30mmHg. The mean arterial pressure and PAP were continuously monitoredusing a Gould 6600 amplifier system (Gould Electronics, Inc., Eastlake,Ohio). Pulmonary capillary wedge pressure, heart rate, and cardiacoutput were intermittently measured at baseline, during U46619 infusion,and before and after inhalation of NO generated using either therespiratory system 10, the respiratory system 100, or NO delivered anddiluted at the same level from a compressed gas cylinder. Cardiac outputwas assessed by thermal dilution as the average of three measurementsafter an intravenous bolus injection of 10 mL of ice-cold salinesolution. Pulmonary vascular resistance index (PVRI), as well as cardiacindex (CI), were calculated using standard formulae. The gas cylindercontained 500 ppm NO diluted in nitrogen.

Example 11: Continuous NO Generation from Air Using the RespiratorySystem 10 on Anesthetized Lambs

The respiratory system 10 was tested with an anesthetized lamb as thepatient 11. A baseline (BL) was generated then the NO generator 14 ofthe respiratory system 10 was triggered to continuously spark (i.e.,generate NO) after U46619 was administered for 30 minutes. The NO waspumped at 5 L/min into the inspiratory line 18. The electrodes 36 werefabricated from iridium-platinum. Once triggered, the controller 33 wasconfigured to spark the electrodes 36 for 4 minutes using the followingsettings: B=35, N=25, P=240 μs; and H=100 μs, which producedapproximately 40 ppm of NO, and then the controller 33 stopped the NOgenerator 14. The test was performed when 21% oxygen was supplied to theinlet 24 of the NO generator 14, when 50% oxygen was supplied to theinlet 24 of the NO generator 14, and compared with NO supplied at thesame concentration to the anesthetized lamb from a gas cylinder.

FIG. 22A shows the mean pulmonary artery pressure (PAP) of theanesthetized lamb for the duration of the tests, and FIG. 22B shows thepulmonary vascular resistance index (PVRI) of the anesthetized lamb forthe duration of the tests. As shown in FIGS. 22A and 22B, during the 4minute window 400 when NO was continuously produced by the NO generator14, PAP and PVRI were rapidly reduced while breathing both 21% and 50%oxygen. Also, the reduction in PAP and PVRI for the NO produced by theNO generator 14 was similar to the reduction in PAP and PVRI for the NOsupplied at the same level by dilution from the gas cylinder. Therefore,the respiratory system 10 can be a viable and equivalent replacement forgas cylinders when administering NO inhalation therapy.

Example 12: Continuous NO Generation from Air Using the RespiratorySystem 100 on Anesthetized Lambs

The respiratory system 100 was tested with an anesthetized lamb as thepatient 11. A baseline (BL) was generated then the NO generator 102 ofthe respiratory system 100 was triggered to continuously spark (i.e.,generate NO) after U46619 was administered for 30 minutes. Theelectrodes 36 were fabricated from iridium-platinum. Once triggered, thecontroller 33 was configured to spark the electrodes 36 for 4 minutesusing the following settings: B=35, N=25, P=240 μs; and H=100 μs, whichproduced approximately 40 ppm of NO, and then the controller 33 stoppedthe NO generator 102. The test was performed when 21% oxygen wassupplied in the inspiratory line 18, when 50% oxygen was supplied in theinspiratory line 18, and when NO was supplied to the anesthetized lambdiluted from a compressed gas cylinder.

FIG. 23A shows the mean pulmonary artery pressure (PAP) of theanesthetized lamb for the duration of the tests, and FIG. 23B shows thepulmonary vascular resistance index (PVRI) of the anesthetized lamb forthe duration of the tests. As shown in FIGS. 23A and 23B, during the 4minute window 402 when NO was continuously produced by the NO generator102, PAP and PVRI were rapidly reduced while breathing both 21% and 50%oxygen. Also, the reduction in PAP and PVRI for the NO produced by theNO generator 102 was similar to the reduction in PAP and PVRI for the NOsupplied by the gas cylinder. Also, the performance of the respiratorysystem 100 was similar to the respiratory system 10. Therefore, therespiratory system 100 can provide a viable and equivalent replacementfor compressed gas cylinders when administering NO inhalation therapy.

Example 13: Intermittent NO Generation from Air Using the RespiratorySystem 100 on Anesthetized Lambs

The respiratory system 100 was tested with an anesthetized lamb as thepatient 11. A baseline (BL) was generated then the NO generator 102 ofthe respiratory system 100 was triggered to intermittently spark (i.e.,generate NO) after U46619 was administered for 30 minutes. Theelectrodes 36 were fabricated from iridium-platinum. The controller 33was configured to spark the electrodes 36 only during the first 0.8seconds of inspiration for 4 minutes using the following settings: B=35,N=25, P=240 μs; and H=100 μs and then the controller 33 stopped the NOgenerator 102. The test was performed when 21% oxygen was supplied inthe inspiratory line 18, when 50% oxygen was supplied in the inspiratoryline 18, and when NO was supplied to the anesthetized lamb from a gascylinder.

FIG. 24A shows the PAP of the anesthetized lamb for the duration of thetests, and FIG. 24B shows the PVRI of the anesthetized lamb for theduration of the tests. As shown in FIGS. 24A and 24B, during the 4minute window 404 when NO was produced during the first 0.8 seconds ofinspiration by the NO generator 102, mean pulmonary artery pressure(PAP) and the pulmonary vascular resistance index (PVRI) were rapidlyreduced breathing either 21% and 50% oxygen. Also, the reduction in PAPand PVRI for the NO produced by the NO generator 102 was similar to thereduction in PAP and PVRI for NO supplied and diluted from thecompressed gas cylinder. Also, the performance of the respiratory system100 when intermittently sparking the electrodes 36 was similar to therespiratory system 100 and the respiratory system 10 when continuouslysparking the electrodes 36. Therefore, intermittently generating NO withthe respiratory system 100 can be a viable replacement for gas cylinderswhen administering NO inhalation therapy.

Whilst the invention has been described above, it extends to anyinventive combination of features set out above or in the followingdescription. Although illustrative embodiments of the invention aredescribed in detail herein with reference to the accompanying drawings,it is to be understood that the invention is not limited to theseprecise embodiments. Furthermore, it is contemplated that a particularfeature described either individually or as part of an embodiment can becombined with other individually described features, or parts of otherembodiments, even if the other features and embodiments make no mentionof the particular feature. Thus, the invention extends to such specificcombinations not already described.

While the invention has been described above in connection withparticular embodiments and examples, the invention is not necessarily solimited, and that numerous other embodiments, examples, uses,modifications and departures from the embodiments, examples and uses areintended to be encompassed by the claims attached hereto. The entiredisclosure of each patent and publication cited herein is incorporatedby reference, as if each such patent or publication were individuallyincorporated by reference herein.

We claim:
 1. An apparatus for generating nitric oxide comprising: one ormore pairs of electrodes; a filter arranged downstream of theelectrodes; a scavenger arranged downstream of the electrodes; one ormore sensors configured to measure at least one of a flowrate of gas, anoxygen concentration upstream of the electrodes, a nitric oxideconcentration downstream of the scavenger, and a nitrogen dioxideconcentration downstream of the scavenger; a controller in communicationwith the electrodes and the one or more sensors and configured to supplyan electrical signal to the electrodes that controls timing and sparkingcharacteristics of the electrodes; and wherein the sparkingcharacteristics of the electrodes determine a concentration of nitricoxide generated by the electrodes.
 2. The apparatus of claim 1, whereinthe electrodes comprise at least one of tungsten carbide, carbon,nickel, iridium, titanium, rhenium, and platinum.
 3. The apparatus ofclaim 1, wherein the electrodes comprise iridium.
 4. The apparatus ofclaim 1, wherein the scavenger is fabricated from calcium hydroxide. 5.The apparatus of claim 1, wherein the one or more sensors include anairway flowmeter arranged downstream of the electrodes, an oxygen sensorarranged upstream of the electrodes, a nitric oxide sensor arrangeddownstream of the scavenger, and a nitrogen dioxide sensor arrangeddownstream of the scavenger.
 6. The apparatus of claim 1, wherein anignition coil is in communication with the controller and theelectrodes.
 7. The apparatus of claim 6, wherein the controller isfurther configured to instruct the ignition coil to supply storedelectrical energy to the electrodes.
 8. The apparatus of claim 1,wherein the electrical signal supplied to the electrodes controls atleast one of a number of electrode spark groups per second, a number ofindividual electrode sparks per spark group, a time between individualelectrode sparks, and a pulse duration.
 9. The apparatus of claim 8,wherein the controller is further configured to vary at least one of thenumber of electrode spark groups per second, the number of individualelectrode sparks per spark group, the time between individual electrodesparks, and the pulse duration in response to feedback from the one ormore sensors.
 10. The apparatus of claim 1, further comprising a gaspump arranged upstream of the electrodes.
 11. The apparatus of claim 1,wherein the one or more sensors provide an indication of inspiration.12. The apparatus of claim 12, wherein the controller is furtherconfigured to supply the electrical signal to the electrodes in responseto detecting inspiration.
 13. The apparatus of claim 1, wherein thefiler is configured to filter particles flowing downstream of theelectrodes with a diameter greater than approximately 0.22 micrometers.14. An apparatus for generating nitric oxide to be integrated into arespiratory system having a breathing apparatus, an inspiratory line,and an airway flowmeter arranged on the inspiratory line, the apparatuscomprising: one or more pairs of electrodes in communication with theinspiratory line; a filter arranged downstream of the electrodes; ascavenger arranged downstream of the electrodes; one or more sensorsconfigured to measure at least one of an oxygen concentration upstreamof the electrodes, a barometric pressure, a nitric oxide concentrationdownstream of the scavenger, and a nitrogen dioxide concentrationdownstream of the scavenger; a controller in communication with theelectrodes, the one or more sensors, and the airway flowmeter, andconfigured to supply an electrical signal to the electrodes thatcontrols timing and sparking characteristics of the electrodes; andwherein the sparking characteristics of the electrodes determine aconcentration of nitric oxide generated by the electrodes.
 15. Theapparatus of claim 14, wherein the electrodes are arranged between aninlet and an outlet, the outlet coupled to the inspiratory line.
 16. Theapparatus of claim 14, wherein the electrodes are at least partiallyintegrated into the inspiratory line.
 17. The apparatus of claim 16,wherein the filter is arranged on the inspiratory line.
 18. Theapparatus of claim 16, wherein the scavenger is arranged on theinspiratory line.
 19. The apparatus of claim 14, wherein the electrodescomprise at least one of tungsten carbide, carbon, nickel, iridium,titanium, rhenium, and platinum.
 20. The apparatus of claim 14, whereinthe electrodes comprise iridium.
 21. The apparatus of claim 14, whereinthe scavenger is fabricated from calcium hydroxide.
 22. The apparatus ofclaim 14, wherein the one or more sensors include an oxygen sensorarranged upstream of the electrodes, a nitric oxide sensor arrangeddownstream of the scavenger, and a nitrogen dioxide sensor arrangeddownstream of the scavenger.
 23. The apparatus of claim 14, wherein anignition coil is in communication with the controller and theelectrodes.
 24. The apparatus of claim 23, wherein the controller isfurther configured to instruct the ignition coil to supply storedelectrical energy to the electrodes.
 25. The apparatus of claim 14,wherein the electrical signal supplied to the electrodes controls atleast one of a number of electrode spark groups per second, a number ofindividual electrode sparks per spark group, a time between individualelectrode sparks, and a pulse duration.
 26. The apparatus of claim 25,wherein the controller is further configured to vary at least one of thenumber of electrode spark groups per second, the number of individualelectrode sparks per spark group, the time between individual electrodesparks, and the pulse duration in response to feedback from the one ormore sensors.
 27. The apparatus of claim 15, further comprising a gaspump arranged upstream of the electrodes.
 28. The apparatus of claim 16,wherein the airway flowmeter provides an indication of inspiration. 29.The apparatus of claim 28, wherein the controller is further configuredto supply the electrical signal to the electrodes in response todetecting inspiration.
 30. The apparatus of claim 14, wherein the filteris configured to filter particles flowing downstream of the electrodeswith a diameter greater than approximately 0.22 micrometers.
 31. Theapparatus of claim 14, wherein the breathing apparatus comprises one ofa ventilator system, a continuous positive airway pressure (CPAP)system, a High Frequency Oscillatory Ventilator (HFOV), a face mask, anasal cannula or an inhaler.
 32. An apparatus for generating nitricoxide to be integrated into a respiratory system having a breathingapparatus and an inspiratory line, the apparatus comprising: a chamberincluding a chamber inlet and at least one or more pairs of electrodesarranged within the chamber; a main chamber configured to provide afluid path to an airway of a patient; a filter arranged downstream ofthe electrodes; a scavenger arranged downstream of the electrodes; oneor more sensors configured to measure at least one of an oxygenconcentration upstream of the electrodes, a barometric pressure, anitric oxide concentration downstream of the scavenger, and a nitrogendioxide concentration downstream of the scavenger; a controller incommunication with the electrodes and the one or more sensors, andconfigured to supply an electrical signal to the electrodes thatcontrols sparking characteristics of the electrodes; and wherein thechamber is in communication with the main chamber and gas in the chamberis non-mechanically induced into the main chamber.
 33. The apparatus ofclaim 32, wherein the main chamber includes a venturi.
 34. The apparatusof claim 33, further comprising a passage connecting the chamber to theventuri of the main chamber.
 35. The apparatus of claim 33, wherein aflow of gas through the venturi is configured to draw a vacuum on thechamber.
 36. The apparatus of claim 32, further comprising apre-scavenger arranged upstream of the chamber inlet.
 37. The apparatusof claim 32, further comprising a pre-filter arranged upstream of thechamber inlet.
 38. The apparatus of claim 32, wherein the main chamberand the chamber define a parallel path.
 39. A method of generatingnitric oxide in a respiratory system having a breathing apparatus incommunication with an airway of a patient, the method comprising:coupling a nitric oxide generator including a pair of electrodes to theairway of the patient; triggering the nitric oxide generator to producea desired concentration of nitric oxide gas; determining desiredsparking characteristics of the electrodes to produce the desiredconcentration of nitric oxide gas; and once the sparking characteristicshave been determined, supplying an electrical signal to the electrodesthat initiates the desired sparking characteristics between theelectrodes to generate the desired concentration of nitric oxide gas ina flow of gas provided to the airway of the patient.
 40. The method ofclaim 39, wherein the breathing apparatus one of a ventilator system, acontinuous positive airway system (CPAP) system, a High FrequencyOscillatory Ventilator (HFOV), a face mask, a nasal cannula or aninhaler.
 41. The method of claim 39, wherein triggering the nitric oxidegenerator to produce a desired concentration of nitric oxide gascomprises: monitoring at least one of a gas flowrate provided to thepatient, a temperature of gas provided to the patient, and a pressure ofgas provided to the patient; detecting a change in at least one of thegas flowrate provided to the patient, the temperature of gas provided tothe patient, and the pressure of gas provided to the patient; anddetermining that the change detected is indicative of an inspiratoryevent.
 42. The method of claim 39, further comprising: filteringparticulates in the flow of gas provided to the patient.
 43. The methodof claim 39, further comprising: scavenging at least one of nitrogendioxide and ozone in the flow of gas provided to the patient.
 44. Themethod of claim 39, wherein determining desired sparking characteristicsof the electrodes comprises: measuring an atmospheric pressure; anddetermining a number of electrode spark groups per second, a number ofindividual electrode sparks per spark group, a time between individualelectrode sparks, and a pulse duration.
 45. The method of claim 39further comprising: monitoring a at least one of a nitric oxideconcentration downstream of the electrodes and a nitrogen dioxideconcentration downstream of the electrodes; determining that at leastone of the nitric oxide concentration and the nitrogen dioxideconcentration is not equal to a desired concentration; and in responseto determining that the nitric oxide concentration downstream of theelectrodes is not equal to the desired concentration, varying, via theelectrical signal, at least one of a number of electrode spark groupsper second, a number of individual electrode sparks per spark group, atime between individual electrode sparks, and a pulse duration.
 46. Themethod of claim 39 further comprising: monitoring a nitrogen dioxideconcentration downstream of the electrodes; determining that thenitrogen dioxide concentration is greater than a pre-defined maximumconcentration; and upon determining that the nitrogen dioxideconcentration downstream of the electrodes is greater than thepre-defined maximum concentration, ceasing the supplying of theelectrical signal to the electrodes.